Printed wiring board, and method and apparatus for manufacturing the same

ABSTRACT

In manufacturing a double-layered or a multi-layered printed wiring board, a layer of metamorphic substance, which is created by transmuting a substrate material, is formed on an inner wall of a hole during a perforation process of the substrate utilizing radiation energy. The layer of metamorphic substance prevents conductive materials constituting electrical connection means formed on the inner wall of the hole from dispersing over a surface of the substrate or permeating into the substrate.

This is a Division of application Ser. No. 09/248,020 filed Feb. 10,1999 now U.S. Pat. No. 6,365,844.

FIELD OF THE INVENTION

The present invention relates to a printed wiring board for use in avarious kinds of electronic equipments, and a method of and an apparatusfor manufacturing the same.

BACKGROUND OF THE INVENTION

Double-layered printed wiring boards and multi-layered printed wiringboards enabling a high-density mounting are being spread widely foradoption in electronic equipment along with reduction in size andincrease in density of the electronic equipment through the years. Inmanufacturing process of the double-layered printed wiring boards andthe multi-layered printed wiring boards, in the past, drilling has beenused to form through holes and blind holes in a substrate. In recentyears, however, a new perforation method utilizing a laser beam isemerging as a process capable of making finer holes at higher speed, asdisclosed in Japanese Patent Laid-Open Publication, No. H09-107168.

In the prior art perforation method utilizing a laser beam, generallythe work has been performed according to a specification for a totalamount of radiation energy to be irradiated in a unit area of asubstrate. However, there have been cases where dispersion occurs as aresult of the work depending on a radiating apparatus, even though thetotal amount of radiation energy is maintained constant.

Further, another perforation method of the prior art utilizing a laseradopts a process in that a substrate material, as a working object, isevaporated instantaneously in the shortest possible time by irradiatingthe substrate material with a laser beam having an enhanced peak energy,in order to reduce an effect of heat to a circumjacent area of the partbeing processed. However, if the prior art method of laser processing isapplied to a substrate having porous structure, a cavity 1 a leading toan interior of the substrate can develop in an inner wall of the throughhole, as shown in FIG. 15B.

Since a purpose of making the through hole is to form an electricconductive means in the through hole by plating, or by using aconductive paste or the like material for making an electrical contactbetween an upper and a lower surfaces of the substrate, a development ofthe cavity 1 a leading to an interior of the substrate causes a problemof deteriorating an insulation property of the printed wiring boardaround the through hole due to an entry of the plated membrane or theconductive paste, as shown in FIG. 16A. A further problem occurs thatreliability of the printed wiring board is impaired, if the cavity 1 ais present near the surface of the substrate, because a materialcomposing the electric conductive means spreads around the through holeon the surface of the printed wiring board as shown in FIG. 16B.

For the above reasons, the present invention aims at providing a printedwiring board having high density and high reliability, and also a methodand an apparatus for manufacturing the printed wiring board of highdensity and high reliability without decreasing the speed of the laserprocessing in the work of perforating the printed wiring board.

SUMMARY OF THE INVENTION

The present invention relates to a double-layered and a multi-layeredprinted wiring board provided with electrical connection meansinterconnecting a plurality of circuits through a through hole or ablind hole formed in a substrate material in order to connect thecircuits constructed with a plurality of metal foils sandwiching aninsulation substrate, and a method and an apparatus for manufacturingthe same. In the manufacturing process of the printed wiring board ofthe present invention, the printed wiring board is provided with apreventive means on an inner wall of the through hole or the blind holefor preventing conductive materials constituting the electricalconnection means from spreading or permeating into or over the surfaceof the substrate material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, 1E, and 1F are a series of figures depicting amanufacturing process of a double-layered printed wiring board of afirst exemplary embodiment of the present invention;

FIGS. 2A and 2B depict a rough figure of a waveform of laser pulse usedfor the prior art laser processing, and a cross sectional view of asubstrate after the processing;

FIGS. 3A and 3AB depict a rough figure of a waveform of the laser pulse,of which peak energy is reduced and an irradiating duration is prolongedin the prior art laser processing, and a cross sectional view of asubstrate after the processing;

FIGS. 4A and 4B depict a rough figure of a waveform of the laser pulseused in a second exemplary embodiment of the present invention, and across sectional view of a substrate after the processing;

FIGS. 5A, 5B, 5C, 5D, 5E, and 5F are a series of figures depicting amanufacturing process of a double-layered printed wiring board of athird exemplary embodiment of the present invention;

FIG. 6 is a rough structural drawing depicting a manufacturing apparatusof a printed wiring board of a fourth exemplary embodiment of thepresent invention;

FIGS. 7A and 7B depict a figure showing an energy distribution of thelaser used in the prior art laser processing, and a cross sectional viewof the processed portion;

FIGS. 8A and 8B depict a figure showing an energy distribution of thelaser used in the fourth exemplary embodiment of the present invention,and a cross sectional view of the processed portion;

FIGS. 9A and 9B depict a figure showing an energy distribution of thelaser, when the laser beam is excessively choked in the fourth exemplaryembodiment of the present invention, and a cross sectional view of theprocessed portion;

FIGS. 10A, 10B, 10C, and 10 are a series of figures depicting amanufacturing process of a multi-layered printed wiring board of a fifthexemplary embodiment of the present invention;

FIGS. 11A, 11B, 11C, and 11D are a series of figures depicting anintermediate manufacturing process of a printed wiring board of a sixthexemplary embodiment of the present invention;

FIGS. 12A, 12B, and 12C are a series of figures depicting anintermediate manufacturing process of a printed wiring board of aseventh exemplary embodiment of the present invention;

FIG. 13 is a rough structural drawing depicting a manufacturingapparatus of a printed wiring board of an eighth exemplary embodiment ofthe present invention;

FIG. 14 is a perspective view depicting a laser oscillator for themanufacturing apparatus of a printed wiring board of a ninth exemplaryembodiment of the present invention;

FIGS. 15A and 15B are a series of figures depicting an intermediatemanufacturing process of a printed wiring board of the prior art;

FIGS. 16A and 16B depict cross sectional views of double-layered printedwiring boards of the prior art; and

FIG. 17 depicts a cross sectional view of a double-layered printedwiring board of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 through FIG. 14, preferred embodiments of thepresent invention will be described hereinafter with an example using asubstrate material made of a composite of aromatic polyamide fiber(i.e., aramid fiber) and thermosetting resin.

First Exemplary Embodiment

FIGS. 1A through 1F are cross sectional views of an area around athrough hole, depicting a manufacturing process of a printed wiringboard of a first exemplary embodiment of the present invention. In FIG.1, a substrate material 11 constituting a base material of the printedwiring board is a composite material composed of epoxy resin 12, whichis a kind of thermosetting resin, and aramid fiber 13. These materialsare normally used in a state that the epoxy resin is partiallypolymerized, which is usually called “B-stage” in the printed wiringboard manufacturing industry. A composite of polymeric resin and fiberin a state of the B-stage is commonly called a “prepreg”, which iscommercially available. The prepreg is generally a porous substancecontaining numerous pores in it. The aramid fiber can be either in awoven form or non-woven form for use in the prepreg. Although aramidfiber is used for the fiber material in the prepreg of the describedembodiment, other organic fiber materials such as various kinds ofpolyester fiber, aliphatic polyamide fiber, phenolic fiber, etc. or anyinorganic fiber material typified by glass fiber can also be used.

A through hole 15 is formed next by irradiating a laser beam 14 to thesubstrate material 11 as shown in FIG. 1B. When the substrate material11 is laser irradiated, the epoxy resin and the aramid fiber in thesubstrate material are dispersed into the surrounding by evaporation andsublimation. If a condition of the laser irradiation is optimized in amanner as to be described in a succeeding second exemplary embodiment,the aramid fiber 13 around a sidewall of the hole is melted to form alayer of metamorphic substance 16 on the sidewall of the hole. Althoughmolten matter of the aramid fiber constitutes a major constituent of themetamorphic substance layer 16, as described above, the epoxy resin 12can also be a part of the constituent elements.

Although the metamorphic substance layer 16 is formed as a relativelydense membrane over the inner wall of the through hole 15, it does notnecessarily cover the entire wall surface uniformly. In other words, ithas been revealed as a result of an experiment conducted by theinventors of this patent that, resin materials contained in conductivepaste 17, which is rubbed into the through hole 15 in the next process,are permeated into an interior of the substrate material 11 via themetamorphic layer 16 of the through hole 15 during the subsequenthot-pressing process. On the other hand, conductive particles havingdiameter of 1 to 5 μm contained in the conductive paste 17 are notpenetrated into the substrate material 11, thereby increasing a densityof the conductive materials within the through hole 15 after thehot-pressing.

The phenomenon that the density of the conductive materials within thethrough hole increase after the hot-pressing, exerts its effectespecially when manufacturing a printed wiring board having throughholes of a small diameter. That is, it requires conductive paste of lowviscosity by increasing an amount of resin content contained in theconductive paste, when the conductive paste is being rubbed into thethrough hole of small diameter. However, if the resin content in theconductive paste is increased, reliability in electrical contact throughthe conductive paste decreases. In this respect, the metamorphicsubstance layer formed according to the present invention improvesreliability in the electrical contact, since the density of theconductive materials within the through hole increases after thehot-pressing, due to permeation of the resin component in the conductivepaste into the substrate material during the hot pressing process asaforecited. In a word, the metamorphic substance layer for the purposeof preventing permeation of the conductive materials, as described inthis invention, needs not be an absolutely perfect layer, but it servesthe purpose if it can prevent the conductive materials composing theelectric connection means from permeating and dispersing into thesubstrate material or the surfaces surrounding the through hole.

Subsequently, the conductive paste 17 as connection means composedmainly of conductive particles and epoxy resin is filled in the throughhole 15, as shown in FIG. 1C, by printing or the similar means. Further,the substrate material 11 is sandwiched with two metal foils 18 on bothsurfaces, as shown in FIG. 1D, and hot-pressed, so that the substratematerial 11 is compression-molded in a direction of thickness. And, as aresult, the metal foils 18 on both sides of the substrate material 11are electrically connected with the conductive particles in theconductive paste 17 as depicted in FIG. 1E.

After the foregoing steps, the metal foils 18 on both sides of thesubstrate material 11 are etched to form a circuit 19 by an ordinaryetching process, and a printed wiring board is completed as shown inFIG. IF.

The present embodiment is especially effective if the substrate material11 is in a state of prepreg having numerous pores, and this invention isalso useful for the printed wiring board utilizing a porous material,which is easy to process with the compression-molding, for the substratematerial 11.

Although the embodiment as described above is a structure of thedouble-layered printed wiring board, it needs no mentioning that amultilayered printed wiring board can be formed by superposing andhot-pressing a plurality of double-layered printed wiring boardsproduced by the foregoing manufacturing method with another substratematerial filled with the conductive paste in the through hole shown inFIG. 1C.

Second Exemplary Embodiment

An experiment was conducted using a carbon dioxide gas laser (“CO₂laser”) as a source of the laser beam in the first exemplary embodiment,with various conditions of the laser beam irradiated on the substratematerial.

First, a substrate material 11 in a thickness of approximately 200 μmwas irradiated with a laser having a high peak energy, which is the samecondition as used for the conventional laser process, for a comparisonpurpose. A sheared cross sectional surface of the aramid fibers in across section of the through hole remained intact, and no effect of theheat was seen in the epoxy resin around the through hole, as shown inFIG. 2B. It was assumed from the above results that the substratematerial has evaporated instantaneously. The same kind of results wereobserved when rise and fall times of the laser pulse were 20 μs or less,and peak energy of the laser beam was 1000 W or greater. Besides, alaser pulse width needed for making the through hole in a diameter ofabout 150 μm in the substrate material 11 of about 200 μm thick wasapproximately 50 μs.

For a further comparison, another experiment was conducted with thelaser beam of reduced peak energy. Since the laser beam had low peakenergy, it needed to lengthen a half-value width of the irradiatingpulse as well as a fall time of the laser beam energy, as shown in FIG.3A, in order to create the hole having a required diameter. In thiscomparative example, an inner wall of the through hole 15 became a roughsurface due to formation of a carbonized layer 29 on the inner wall ofthe through hole 15 by carbonization of the aramid fiber 13 and theepoxy resin 12, as shown in FIG. 3B. The same kind of results were alsoobserved when rise and fall times of the laser pulse were 1 ms orlonger, and peak energy of the laser beam was 100 W or smaller.

When a laser irradiation was applied in the next step with a conditionintermediate between the two preceding comparative examples, as shown inFIG. 4A, a membrane-like metamorphic substance layer 16 was formed on aninner wall of the through hole 15 by molten constituent of the aramidfiber 13, as shown in FIG. 4B. Also, when the substrate material 11 wasirradiated with the laser in the above condition, there was not a casewhere a cavity 11 a contained within the substrate material of prepregexposes through the inner wall of the through hole. In addition, themetamorphic substance layer 16 was efficiently formed, when aramidfibers which start shrinking at the temperature of from 150° C. to 300°C. were used, because shrinkage of the fibers occurred due to the effectof heat by the laser irradiation.

Although it was assumed without doubt that component of the epoxy resin12 is partly mixed in the metamorphic substance layer 16, it did notinfluence the effect of the metamorphic substance layer 16 to preventpenetration of the conductive materials. There were also cases that,when other kinds of thermosetting resin, including epoxy resin, are usedfor the substrate material 11, the thermosetting resin supplements voidsdeveloped in the metamorphic substance layer 16 formed by the moltenaramid fibers, and exerts a good influence to the penetration preventiveeffect.

According to the foregoing results, it was found that a condition of thelaser irradiation suitable for the present invention lies between 100 Wand 1000 W in peak energy of the laser beam, 50 μs and 1 ms inhalf-value width of the irradiating laser pulse, and 20 μs and 1 ms infall time of the laser beam. Also, an optimum irradiating condition forthe aramid-epoxy substrate in a thickness of 200 μm was 500 W in peakenergy of the laser beam, 250 μs in half-value width of the irradiatinglaser pulse, and 50 μs in fall time of the laser beam, with which afavorable metamorphic substance layer 16 was produced. The satisfactorymetamorphic substance layer was obtained in the substrate not only withthe aforecited single condition, but also with a condition of 400 W inpeak energy of the laser beam, 500 μs in half-value width of theirradiating laser pulse, and 300 μs in fall time of the laser beam,indicating that the satisfactory metamorphic substance layer isobtainable in a wide range of irradiating condition. Incidentally, theaforecited fall time is defined as a time required for the laser energyto decrease to 1/e² (approximately 13.5%, where “e” is the base of thenatural logarithms).

It is desirable to determine a minimum energy that does not produce acarbonized layer on the inner wall of the through hole by examining peakpower of the laser beam and time of the irradiating pulse in advance forthe substrate material to be used, since the optimum processingcondition varies, as has been described, depending on material andthickness of the substrate material. A desirable metamorphic substancelayer is attained by adjusting the fall time of the laser energy withina range of approximately 50% to 200% of the half-value width of theirradiating pulse, on top of the above.

Since there are often cases wherein adjusting ranges for the peak powerand the irradiating pulse time are limited by a structure of the lasergeneration source, it is effectual to use a mask or the like means in apath of the laser beam in order to adjust a magnitude of energy, as willbe described later.

Third Exemplary Embodiment

FIGS. 5A through 5F depict cross sectional views showing a manufacturingprocess of a printed wiring board of a third exemplary embodiment of thepresent invention. This exemplary embodiment differs from the firstexemplary embodiment in that the substrate material 11 is composedsolely of the thermosetting resin 12 in a state of the B-stage, withoutincluding fiber material for reinforcement. In a material of this kind,there are instances where conductive materials in a through holedisperse into the substrate material 11 nearby the through hole, as thethermosetting resin melts by heat. This dispersion of the conductivematerials can be prevented, in the same manner as the first exemplaryembodiment, by forming the metamorphic substance layer 16 on the innerwall of the through hole. While it can be assumed that the metamorphicsubstance layer 16 in the present embodiment is composed of substanceproduced through a progression of hardening of the thermosetting resin,the similar effect can be exerted with certain thermoplastic resins insome instances.

Fourth Exemplary Embodiment

FIG. 6 is a brief structural drawing depicting a manufacturing apparatusfor a printed wiring board of the present invention. In FIG. 6, a laserbeam 14 emitted by a laser beam oscillator 20 is adjusted to a requiredbeam diameter by introducing to a mask 21 via a total reflection miller22, etc, and irradiated on a substrate material 11 by a condensing lens24 after passing through a scanner means 23 for scanning the laser beam.A galvanomiller is generally used for the scanner means 23. Thesubstrate material 11 is moved by an X-Y stage or the like means (notshown in the figure) so that a targeted position for irradiation isirradiated with the laser.

With reference to FIG. 7 through FIG. 9, an irradiating condition, etc.of the laser beam will be described hereinafter.

For a comparison purpose, FIG. 7 depicts a metamorphic substance layer,which is formed when an ordinary unprocessed laser beam is used. Theordinary laser beam has energy distribution as shown in FIG. 7A in thatthe energy decreases gradually toward a radial direction, with a centerbeing the highest. When the laser beam as shown here is irradiated onthe substrate material 11, a through hole 15 as well as a metamorphicsubstance layer 16 in vicinity of the through hole 15 are formed in thesubstrate material 11 due to a thermal effect of the laser beam.However, since the energy is small around the perimeter of the laserbeam, the substrate material 11 can not be eliminated by evaporation,thereby leaving a thick metamorphic substance layer on the surface areaof the substrate material 11 surrounding the through hole 15.

The thick metamorphic substance layer existing in the substrate material11 impedes a hot pressing process, and a resultant insufficiency ofcompression in the through hole area reduces reliability of theelectrical contact of the electrical connection means formed in thethrough hole 15. Adoption of the mask 21 is effective in solving thisproblem, as it cuts off the low energy area of the laser beam, as shownin FIG. 6.

As shown in FIG. 8A, properly cutting off the part of low energy aroundthe perimeter of the laser beam with the mask can realize formation of athin and uniform metamorphic substance layer 16 around the inner wall ofthe through hole 15. Furthermore, a result is shown in FIG. 9, in whichthe laser beam is excessively cut off. As shown in FIG. 9B, thesubstrate material 11 does not develop a metamorphic substance layer,when it is irradiated with only a part of high energy in the center ofthe laser beam shown in FIG. 9A. Consequently, conductive materialscomposing the electrical connection means disperse or permeate into thesubstrate material 11 in vicinity of the through hole 15.

According to an experiment conducted by the inventors, theunsatisfactory phenomenon as shown in FIG. 9 was observed when 98% ormore of the laser beam around the perimeter was cut off. It was alsoobserved, however, when an irradiating time of the laser was prolonged,the hole diameter increased gradually due to the effect of heat from thelaser beam 14, and the metamorphic substance layer 16 of the presentinvention was eventually formed on the inner wall, even if perimeter ofthe laser beam was cut off by 98% or more.

From a result of the experiment, it was found that a good metamorphicsubstance layer is formed on the inner wall of the through hole 15, ifthe laser beam is irradiated on the substrate material 11 for a durationthat produces a diameter of the through hole 15 in a range of 110% to300% of a diameter of the laser beam. In other words, a favorablemetamorphic substance layer can be formed with an irradiation of a laserof only the high energy portion, if the laser beam in a diameter ofapproximately 30% to 90% of the designed hole diameter is irradiated.

Although the embodiment as described above is a case that the laser beamis adjusted with the mask 21 as shown in FIG. 6, the mask 21 may not beneeded in certain instances where quality of the laser beam oscillatoris exceedingly well. This is because the part carrying a small energyaround perimeter of the laser beam has an amount of energy suitable forthe formation of metamorphic substance layer, in these instances.

As has been described in the foregoing exemplary embodiments, amagnitude of the laser irradiation required for producing the favorablemetamorphic substance layer is the sum of a minimum energy necessary toform a through hole or a blind hole, and an energy to form themetamorphic substance layer. It is effective, as concrete means forapplying the energy to form the metamorphic substance layer, to eitherprolong the irradiation time or a fall time of the laser pulse, orutilize an energy density distribution of the laser beam.

Fifth Exemplary Embodiment

FIGS. 10A through 10D depict cross sectional views of an area around ablind hole showing a manufacturing process of a multi-layered printedwiring board of a fifth exemplary embodiment of the present invention.In this exemplary embodiment, a material constructed of a double-layeredprinted wiring board pre-formed with an electric circuit 25 superposedby an insulation layer 12 composed of aramid fiber and thermosettingresin, as shown in FIG. 10A, is used for the substrate material 11.Next, a blind hole 26 is formed by irradiating a laser beam (not shown)on the insulation material in an area over the electric circuit in thesubstrate material 11, as shown in FIG. 10B. A metamorphic substancelayer 16 can be produced on an inner wall of the blind hole 26 byproperly setting an irradiating condition of the laser during thisprocess.

Since metal foil has low absorption coefficient for the ordinary laserbeam, the laser beam is able to form the blind hole only in theinsulation material 12 without impairing the metal foil in theperforating process. A variety of gas lasers typified by the CO₂ laser,solid-state lasers represented by the YAG laser, a variety of excimerlasers, and the like can be utilized for a laser source in the presentembodiment.

A metal layer 27 for an outer layer circuit connected with the innerlayer circuit 25 is formed by the known methods of electroless platingand electroplating on a surface of the substrate material 11 formed withthe metamorphic substance layer 16, as shown in FIG. 10C. And further,the outer layer circuit is formed with a patterning process so as tocomplete a four-layered printed wiring board as shown in FIG. 10D.

The metamorphic substance layer 16 of the present invention effectivelyprevents plating solution from permeating into the substrate materialduring the plating process.

Sixth Exemplary Embodiment

FIGS. 11A through 11D depict cross sectional views of an area around athrough hole showing a manufacturing process of a multilayered printedwiring board of a sixth exemplary embodiment of the present invention.In this exemplary embodiment, a substrate material 11 in a board-form ismade of thermosetting resin 12, which is laminated on both surfaces withresin films 31 such as polyethylene terephthalate as shown in FIG. 11A.Next, a through hole 15 is formed as shown in FIG. 11B, by a laser beam14.

A resin layer 32 is then formed by either dipping or spraying methods onthe surface of the substrate material 11 and inner wall of the throughhole 15 as shown in FIG. 11C. Thermosetting resin or the like materialdiluted by solvent is suitable for a material of the resin layer 32. Itis desirable to increase a hardness of the resin layer 32 by removingthe solvent in a drying furnace after the substrate material 11 iscoated with the resin solution. The substrate material 11 formed withthe resin layer 32 on only the inner wall of the through hole 15 is thusobtained by removing the resin film 31 as shown in FIG. 11D.

The resin layer 32 as is formed in this manner has the same function asthe metamorphic substance layer 16 described in the third exemplaryembodiment of the present invention, which is capable of preventing theconductive materials composing an electrical connection means fromdispersing in vicinity of the through hole 15 in the succeedingprocesses. Although the described embodiment utilizes a resin film forpreventing dispersion of the conductive materials composing theelectrical connection means, this does not limit to resin film as thematerial having this nature of function, and the same effect isattainable with a membrane formed on the inner wall of the through holeby spattering or the like method.

Seventh Exemplary Embodiment

FIGS. 12A through 12C depict cross sectional views of an area around athrough hole showing a manufacturing process for a multilayered printedwiring board of a seventh exemplary embodiment of the present invention.In this exemplary embodiment, a substrate material 11 in a board-form ismade of thermosetting resin 12 in a state of the B-stage. A through hole15 is formed in the substrate material 11 using a laser beam 14 as shownin FIG. 12B. Then, conductive paste 17 is filled in the through hole 15as shown in FIG. 12C.

The present embodiment is peculiarized by a hardening agent for thethermosetting resin, which constitutes the substrate material 11, addedto the conductive paste 17. The hardening agent for the thermosettingresin causes a reaction with the thermosetting resin 12 in a state ofthe B-stage to form a hardened resin layer 33 in vicinity of an innerwall of the through hole 15. The hardened resin layer 33 can be formedon the inner wall of the through hole 15 before the substrate materialhardens, by adding into the conductive paste 17 the hardening agent thathas a higher reactivity than a hardening agent in the thermosettingresin 12 in a state of the B-stage. The hardened resin layer 33 exerts agood effect to prevent dispersion of the conductive materials in theconductive paste to an interior of the substrate material.

Eighth Exemplary Embodiment

FIG. 13 is a brief structural drawing depicting a manufacturingapparatus for a printed wiring board of an eighth exemplary embodimentof the present invention. A laser beam 14 induced by a laser beamoscillator 20 enters into a shutter 34 via a total reflection miller 22,etc, and is irradiated on a substrate material 11 by a condensing lens24 after passing through a scanner means 23. A pulse width of the laserbeam 14 to be irradiated on the substrate material 11 is adjustable to adesired value by opening and closing the shutter 34. The scanner means23, the substrate, etc. shown in FIG. 13 move in the same manner as inthe case of the fourth exemplary embodiment.

With regard to controlling an irradiation time of the laser beam,although it is feasible to adjust a pulse width of the laser beam 14 byvarying a pulse width of an oscillation dictating signal to be input tothe laser beam oscillator 20, the shutter 34 gives a higher degree offreedom in adjusting the pulse width. It is even more preferable tocontrol the laser beam 14 by dictating two parameters, i.e. the pulsewidth of the oscillation-dictating signal, and opening and closing timesof the shutter 34.

A through hole having a metamorphic substance layer suitable for thepurpose of this invention was attained, when a laser beam was irradiatedfor the time necessary to obtain the through hole in diameter of 110% to300% of the laser beam diameter, in addition to the time needed toeliminate the substrate material 11 irradiated with the laser beam 14using the manufacturing apparatus for printed wiring boards of thepresent embodiment.

Furthermore, a through hole having a metamorphic substance layersuitable for the purpose of this invention was also attained, when apulse width of the laser beam irradiated on the substrate material 11was set within 50 μs and 1 ms in half-value width.

Ninth Exemplary Embodiment

FIG. 14 is a perspective view depicting a laser oscillator of amanufacturing apparatus for a printed wiring board of an ninth exemplaryembodiment of the present invention. In the laser oscillator, a voltageis applied between an upper and a lower discharge electrodes 35, andlaser medium gas flows at a constant velocity in a direction of the gasflow 38. A laser beam is generated from gas molecules 36 excited betweenthe electrodes, emitted as a laser beam 37 after amplified in anaperture 39. For this reason, an oscillation of the laser beam continuesuntil the excited gas molecules are expelled by the gas flow from theaperture space, even after the discharge voltage is turned off. The falltime can be controlled by taking advantage of this principle. Anexperiment yielded a favorable metamorphic substance layer around athrough hole perforated by the laser, since the fall time of the laserbeam became 300 μs, when the discharge electrodes were 50 mm in width,the aperture was positioned in the center of the electrodes, and avelocity of the gas was set for 80 m/s.

What is claimed is:
 1. A method of manufacturing a printed wiring boardcomprising the steps of: perforating a through hole or a blind hole byirradiating an amount radiation energy on a substrate in a form of boardor sheet composite of either a single or a plurality of materials toform a layer of metamorphic substance at least on an inner wall of saidhole with one or more constituent elements of said substrate; forming aconnection means in the hole formed in said perforation step forelectrically connecting an upper and a lower surfaces of the substrate;hot-pressing at least two layers of metal foil to sandwich at least saidsubstrate; and patterning said at least two layers of metal foil,wherein layer of metamorphic substance prevents conductive substanceconstituting said electrical connection means from dispersing orpermeating into an interior of the substrate or over a surface thereof.2. The method of manufacturing a printed wiring board according to claim1, wherein said radiation energy is obtained by way of a laser beam. 3.The method of manufacturing a printed wiring board according to claim 2,wherein a source of generating said laser beam comprises a carbondioxide gas laser.
 4. A method of manufacturing a printed wiring boardaccording to claim 2, wherein a pulse width of the laser beam irradiatedon the substrate is in a range of 50 μs and 1 ma in half-value width. 5.The method of manufacturing a printed wiring board according to claim 2,wherein peak energy of the laser beam irradiated on the substrate iswithin 100 W and 1000 W.
 6. The method of manufacturing a printed wiringboard according to claim 1, wherein said step of forming an electricalconnection means includes a step of filling conductive paste containingconductive particles in the hole formed in the perforation step.
 7. Themethod of manufacturing a printed wiring board according to claim 1,wherein said step of forming an electrical connection means within thehole includes a step of plating metal.
 8. The method of manufacturing aprinted wiring board according to claim 1, wherein at least a perforatedarea of the substrate comprises a resin film containing unhardenedresin.
 9. The method of manufacturing a printed wiring board accordingto claim 8, wherein the resin comprises thermosetting resin.
 10. Themethod of manufacturing a printed wiring board according to claim 9,wherein the resin is in a state of B-stage.
 11. The method ofmanufacturing a printed wiring board according to claim 1, wherein thesubstrate comprises a composite material of woven fiber or non-wovenfiber and a resin.
 12. The method of manufacturing a printed wiringboard according to claim 11, wherein the resin comprises thermosettingresin.
 13. The method of manufacturing a printed wiring board accordingto claim 12, wherein the resin is in a state of B-stage.
 14. The methodof manufacturing a printed wiring board according to claim 11, whereinthe woven fiber or the non-woven fiber is made of organic fibermaterial.
 15. The method of manufacturing a printed wiring boardaccording to claim 14, wherein the organic fiber material comprisesaromatic polyamide fiber.
 16. The method of manufacturing a printedwiring board according to claim 14, wherein the organic fiber materialhas a shrinkage start-up temperature Within 150° C. and 300° C.
 17. Themethod of manufacturing a printed wiring board according to claim 11,wherein the layer of metamorphic substance on the inner wall of the holecomprises a transmuted component of the woven fiber or the non-wovenfiber.
 18. The method of manufacturing a printed wiring board accordingto claim 11, wherein the layer of metamorphic substance on the innerwall of the hole comprises metamorphic substance developed incombination of a transmuted component of the woven fiber or thenon-woven fiber and a component of polymeric resin composing thesubstrate.
 19. The method of manufacturing a printed wiring boardaccording to claim 11, wherein the substrate comprises a porousmaterial.
 20. A method of manufacturing a primed wiring board comprisingthe steps of: perforating a through hole or a blind hole by irradiatingan amount radiation energy on a substrate in a form of board or sheetcomposite of either a single or a plurality of materials; formingconnection means in the hole formed in said perforation step toelectrically connect an upper and a lower surfaces of the substrate;hot-pressing at least two layers of metal foil to sandwich at least saidsubstrate; and patterning said at least two layers of metal foil,wherein any one of said perforation step and the succeeding stepsfurther including step of forming a prevention means for preventingconductive substance constituting said electrical connection means fromdispersing or permeating into an interior of the substrate or over asurface thereof, and wherein a total sum of the radiation energyrequired for perforating one hole is: less than a sum of a minimumamount of energy necessary for perforating the hole in a desireddiameter and a minimum amount of energy necessary for forming a layer ofmetamorphic substance other than carbonized substance on an inner wallof the hole; and not more than an amount of energy necessary for forminga layer of carbonized substance on the inner wall of the hole.
 21. Amethod of manufacturing a printed wiring board comprising the steps ofperforating a through hole or a blind hole by irradiating an amountradiation enemy on a substrate in a form of board or sheet composite ofeither a single or a plurality of materials; forming a connection meansin the hole formed in said perforation step for electrically connectingan upper and a lower surfaces of the substrate; hot-pressing at leasttwo layers of metal foil to sandwich at least said substrate; andpattering said at least two layers of metal foil. wherein any one ofsaid perforation step and the succeeding steps further includes a. stepof forming a prevention means for preventing conductive substanceconstituting said electrical connection means from dispersing orpermeating into an interior of the substrate or oven surface thereof,wherein said radiation energy is obtained by way of a laser beam, andwherein a diameter of the laser beam irradiated on the substrate iswithin 30% and 90% of a designed diameter of the hole.
 22. A method ofmanufacturing a printed wiring board comprising the steps of:perforating a through hole or a blind hole by irradiating an amountradiation energy on a substrate in a form of board or sheet composite ofeither a single or a plurality of materials; forming connection means inthe hole formed in said perforation step for electrically connecting anupper and a lower surfaces of the substrate; hot-pressing at least twolayers of metal foil to sandwich at least said substrate; and patterningsaid at least two layers of metal foil, wherein any one of saidperforation step and the succeeding steps further includes a step offorming a prevention means for preventing conductive substanceconstituting said electrical connection means from dispersing orpermeating into an interior of the substrate or over a surface thereof,wherein said radiation energy is obtained by way of a laser beam, andwherein a pulse width of the laser beam irradiated on the substrate is asum of a time necessary for eliminating the substrate material in anirradiated portion, and a time necessary for creating a hole in diameterof 110% to 300% of the laser beam diameter at a surface of the substratewhile the hole diameter expands progressively due to en exertion of heataround the eliminated portion of the substrate.
 23. A method ofmanufacturing a printed wiring board comprising the steps of:perforating a through hole or a blind hole by irradiating an amountradiation energy on a substrate in a form of board or sheet composite ofeither a single or a plurality of materials; forming a connection meansin the hole formed in said perforation step for electrically connectingan upper and a lower surfaces of the substrate: hot-pressing at leasttwo layers of metal foil to sandwich at least said substrate; andpatterning said at least two layers of metal foil, wherein any one ofsaid perforation step and the succeeding steps further includes a stepof forming a prevention means for preventing conductive substanceconstituting said electrical connection means from dispersing orpermeating into an interior of the substrate or over a surface thereof,wherein said radiation energy is obtained by way of a laser beam, andwherein a fall time of energy of the laser beam irradiated on thesubstrate is within 50% and 200% of a time of the half-value width ofthe peak value.
 24. A method of manufacturing a printed wiring boardcomprising the steps of: perforating a through hole or a blind hole byirradiation an amount radiation enemy on a substrate in a form of boardor sheet composite of either a single or a plurality of materials;forming a connection means in the hole formed in said perforation stepfor electrically connecting an upper and a lower surfaces of thesubstrate: hot-pressing at least two layers of metal foil to sandwich atleast said substrate; and patterning said at least two layers of metalfoil, wherein any one of said perforation step and the succeeding stepsfurther includes a step of forming a prevention means for preventingconductive substance constituting said electrical connection means fromdispersing or permeating into an interior of the substrata or over asurface thereof, wherein said radiation energy is obtained by way of alaser beam, and wherein a fall time of energy of the laser beamirradiated on the substrate is within 20 μs and 1 ms.
 25. A method ofmanufacturing a printed wiring board comprising the steps of:perforating a through hole or a blind hole by irradiating an amountradiation energy on a substrate in a form of board or sheet composite ofeither a single or a plurality of materials; forming a connection meansin the hole formed in said perforation step for electrically connectingan upper and a lower surfaces of the substrate; hot-pressing at leasttwo layers of metal foil to sandwich at least said substrate; andpatterning said at least two layers of metal foil, wherein any one ofsaid perforation step and the succeeding steps further includes a stepof forming a prevention means for prevention conductive substanceconstituting said electrical connection means from dispersing orpermeating into an interior of the substrate or over a surface thereof,wherein said radiation energy is obtained by way of a laser beam, andwherein energy generated by the laser generation source is cut off witha mask by a maximum of 98%.
 26. A method of manufacturing a printedwiring board comprising the steps of: perforating a through hole or ablind hole on a substrate in a form of board or sheet composed of eithersingle or a plurality of materials; forming a layer of metamorphicsubstance at least on an inner wall of said hole with one or moreconstituent elements of said substrate for preventing conductivematerials constituting an electrical connection means from dispersing orpermeating into an interior of the substrate material or over a surfacethereof; forming the electrical connection means in the hole formed insaid perforation step; for electrically connecting an upper and a lowersurfaces of the substrate; and hot-pressing at least two layers of metalfoil to sandwiching at least said substrate.
 27. The method ofmanufacturing a printed wiring board according to claim 26, wherein saidstep of forming an electrical connection means includes a step offilling conductive paste containing conductive particles in the holeformed in the perforation step.
 28. The method of manufacturing aprinted wiring board according to claim 27, wherein a component ratio ofthe conductive particles in the conductive paste within the holeincreases as a result of the hot-pressing step.
 29. The method ofmanufacturing a printed wiring board according to claim 27, wherein saiddispersion prevention means carries voids that allow components otherthan the conducive particles contained in the conductive paste to passthrough, but not allow passage of the conductive particles in a certainextent.
 30. The method of manufacturing a printed wiring board accordingto claim 26, wherein said step of forming an electrical connection meanswithin the hole includes a step of plating metal.
 31. The method ofmanufacturing a printed wiring board according to claim 26, wherein atleast a perforated area of the substrate comprises a resin filmcontaining unhardened resin.
 32. The method of manufacturing a printedwiring board according to claim 31, wherein the resin comprisesthermosetting resin.
 33. The method of manufacturing a printed wiringboard according to claim 32, wherein the resin is in a state of B-stage.34. The method of manufacturing a printed wiring board according toclaim 26, wherein the substrate comprises a composite material of wovenfiber or non-woven fiber and a resin.
 35. The method of manufacturing aprinted wiring board according to claim 34, wherein the resin comprisesthermosetting resin.
 36. The method of manufacturing a printed wiringboard according to claim 35, wherein the resin is in a state of B-stage.37. The method of manufacturing a printed wiring board according toclaim 34, wherein the woven fiber or the non-woven fiber is made oforganic fiber material.
 38. The method of manufacturing a printed wiringboard according to claim 37, wherein the organic fiber materialcomprises aromatic polyamide fiber.
 39. The method of manufacturing aprinted wiring board according to claim 37, wherein the organic fibermaterial has a shrinkage start-up temperature within 150° C. and 300° c.40. The method of manufacturing a printed wiring board according toclaim 34, wherein the layer of metamorphic substance on the inner wallof the hole comprises a transmuted component of the woven fiber or thenon-woven fiber.
 41. The method of manufacturing a printed wiring boardaccording to claim 34, wherein the layer of metamorphic substance on theinner wall of the hole comprises combination of a transmuted componentof the woven fiber or the non-woven fiber and a component of polymericresin composing the substrate.
 42. The method of manufacturing a printedwiring board according to claim 34, wherein the substrate comprises aporous material.
 43. A method of manufacturing a primed wiring boardcomprising steps of: a) perforating a through hole or a blind hole byirradiating an amount of radiation energy on a substrate in a form ofboard or sheet composed of either a single or a plurality of materials;b) forming an electrical connection means in the formed in saidperforation step for electrically connecting an upper and a lowersurfaces of the substrate; and c) hot-pressing at least two layers ofmetal foil sandwiching at least said substrate, wherein one or morecomponents of the material constituting said electrical connection meansreact or combine with said substrate material to form a dispersionprevention means in vicinity of an inner wall of said hole.
 44. Themethod of manufacturing a printed wiring board according to claim 43,wherein said step of forming an electrical connection means includes astep of filling conductive paste containing conductive particles in thehole formed in the perforation step.
 45. The method of manufacturing aprinted wiring board according to claim 27, wherein said layer ofmetamorphic substance carries voids that allow components other than theconductive particles contained in the conductive paste to pass through,but not allow passage of the conductive particles in a certain extent.46. The method of manufacturing a printed wiring board according toclaim 44, wherein a component ratio of the conductive particles in theconductive paste within the hole increases as a result of thehot-pressing step.
 47. The method of manufacturing a printed wiringboard according to claim 43, wherein said step of forming an electricalconnection means within the hole includes a step of plating metal. 48.The method of manufacturing a printed wiring board according to claim43, wherein at least a perforated area of the substrate comprises aresin film containing unhardened resin.
 49. The method of manufacturinga printed wiring board according to claim 48, wherein the resincomprises thermosetting resin.
 50. The method of manufacturing a printedwiring board according to claim 49, wherein the resin is in a state ofB-stage.
 51. The method of manufacturing a printed wiring boardaccording to claim 43, wherein the substrate comprises a compositematerial of woven fiber or non-woven fiber and a resin.
 52. The methodof manufacturing a printed wiring board according to claim 51, whereinthe resin comprises thermosetting resin.
 53. The method of manufacturinga printed wiring board according to claim 52, wherein the resin is in astate of B-stage.
 54. The method of manufacturing a printed wiring boardaccording to claim 51, wherein the woven fiber or the non-woven fiber ismade of organic fiber material.
 55. The method of manufacturing aprinted wiring board according to claim
 54. wherein the organic fibermaterial comprises aromatic polyamide fiber.
 56. The method ofmanufacturing a printed wiring board according to claim 54, wherein theorganic fiber material has a shrinkage start-up temperature within 150°C. and 300° C.
 57. The method of manufacturing a printed wiring boardaccording to claim 51, wherein the dispersion prevention means on theinner wall of the hole comprises a transmuted component of the wovenfiber or the non-woven fiber.
 58. The method of manufacturing a printedwiring board according to claim 51, wherein the dispersion preventionmeans on the inner wall of the hole comprises metamorphic substancedeveloped in combination of a transmuted component of the woven fiber orthe non-woven fiber and a component of polymeric resin composing thesubstrate.
 59. The method of manufacturing a printed wiring boardaccording to claim 51, wherein the substrate comprises a porousmaterial.
 60. A method of manufacturing a printed wiring boardcomprising the steps of: perforating a through hole or a blind hole byirradiating an amount radiation energy on a substrate in a form of boardor sheet composite of either a single or a plurality of materials;forming a connection means in the hole formed in said perforation stepfor electrically connecting an upper and a lower surfaces of thesubstrate; hot-pressing at least two layers of metal foil, patterningsaid at least two layers of metal foil, wherein any one of saidperforation step and the succeeding steps further includes a step offorming a prevention means for preventing conductive substanceconstituting said electrical connection means from dispersing orpermeating into an interior of the substrate or over a surface thereof,wherein said step of in an electrical connection means includes a stepof filling conductive paste containing conductive particles in the holeformed in the perforation step, and wherein said dispersion preventionmeans carries voids that allow components other than the conductiveparticles contained in the conductive paste to pass through, but notallow passage of the conductive particles in a certain extent.
 61. Amethod of manufacturing a printed wiring board comprising the steps of:perforating a through hole or a blind hole by irradiating an amountradiation energy on a substrate in a form of board or sheet composite ofeither a single or a plurality of material; forming a connection meansin the hole formed in said perforation step for electrically connectingan upper and a lower surfaces of the substrate; hot-pressing at leasttwo layers of metal foil to sandwich at least said substrate; andpatterning said at least two layers of metal foil, wherein any one ofsaid perforation step and the succeeding steps further includes a stepof forming a prevention means for preventing conductive substanceconstituting said electrical connection means from dispersing orpermeating into an interior of the substrate or over a surface thereof,wherein said step of forming an electrical connection means includes astep of filling conductive paste containing conductive particles in thehole formed in the perforation step, and wherein a component ratio ofthe conductive particles in the conductive paste within the holeincreases as a result of the hot-pressing step.